The standard practice for fitting such prostheses requires first the fitting of a jersey sheath which is threaded over the stump like a sock. The sheath is much longer than the stump and its free end is threaded through the interior of the nest of the prosthesis and out through the air extraction valve opening at the closed end of the nest, as close as possible to the longitudinal axis of the latter. The amputee, or more usually a third person, then pulls on the free end of the jersey sheath protruding from the nest to compress the flesh of the stump and then to cause it to enter the nest and finally to extract the jersey sheath entirely from the prosthesis, by causing it to slide between the flesh of the stump and the inside wall of the nest.
The drawbacks of this fitting method are as follows:
the traction force to be exerted on the free end of the jersey sheath is far from negligible and is difficult even for a non-handicapped third person; exerting this force becomes extremely difficult or even impossible for an amputee, especially an elderly person or one fatigued by their handicap or who has difficulties in using their hands; this very high traction force requires the jersey sheath to be gripped very strongly by the hand of the person carrying out the operation, and it is often necessary to loop the material around the hand to be able to pull on it effectively; this is very tiresome, especially for rehabilitation center staff who have to repeat this operation several times daily during rehabilitation sessions; in difficult cases it is very often necessary to pull on some specific part of the circumference of the jersey sheath to cause it to slip preferentially on generatrices in contact with the softer tissues;
the direction in which the traction force must be applied is, from the ergonomical point of view, hardly compatible with human anatomy; it is easier to pull towards the body rather than away from it; for this reason there have been proposed devices with a pulley wheel and block and tackle arrangement pressed onto the floor by the sound foot of a lower limb amputee in order to reverse the direction of the force and to reduce it through the mechanical advantage of this device (see the patent FR 2.506,150, for example); systems of this kind have not been widely adopted because they apply to special cases and do not solve the problem of guiding the prosthesis during fitting.
The same applies to devices of the type including a motor resting on the floor, controlled by the amputee and having a shaft around which the jersey sheath can be wound and unwound, as described in the U.S. Pat. No. 3.922,727.
As previously mentioned, during the fitting of the prosthesis it is also necessary to hold the prosthesis and to guide it towards the stump. This is because the friction forces due to movement of the jersey sheath through the air extraction valve opening tend to draw the nest away from the stump rather than towards it.